In the encoding, typically magnetic encoding, of identification cards, as for example credit cards, it is important that the coding imparted to the longitudinal magnetic strip on the card be accurately and precisely spaced along the longitudinal length of the magnetic stripe. It is current practice to have cards encoded at a multitude of stations operated by a variety of operators having varying skill and aptitude. Typically the cards are moved along a slot in an encoding machine or mechanism and the code is imparted along the length of the magnetic stripe by one or more writing heads an one or more tracks. The cards are typically moved manually along the slot, with inevitable variation in card velocity. Since it is important that the coding be imparted to the stripe at precise points along the stripe, it is necessary to provide some mechanism for accurately and precisely sensing the instantaneous longitudinal spatial position of the card as it moves along the slot.
U.S. Pat. No. 3,914,789 of Coker describes a sensing wheel or timing disc which is rotated by frictional contact with the card as the card moves along the slot. The timing disc is provided with visible timing marks adjacent its circumference which are sensed or read out by a photosensor as the wheel is rotated. Rotation of the wheel is done by a hub axially connected to the wheel which is of appreciably smaller diameter than the wheel itself. The circumference of the hub bears against the card, and is turned thereby. Use of optical or visible indicators necessitates the employment of a relatively large wheel in order to achieve the necessary annular separation and resolution between the timing marks. Were the timing wheel itself to bear against the card, the circumference needed to accommodate a sufficient number of timing indices would be much larger than the length of the magnetic stripe on the card--hence, the necessity for driving the timing wheel through a significantly smaller driving hub which actually contacts the card itself.